Biology HL IA - Photosynthesis of elodea lab report

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Biology HL

Candidate name: Ieva Drūlytė

Date: ___________________

Effect of light intensity on the rate of photosynthesis of elodea



Plants and some other organisms use a process called photosynthesis to produce all their own organic substances.  The equation of Photosynthesis:  Water + Carbon Dioxide (With the use of Chlorophyll and Light energy) → Glucose + Oxygen.  Photosynthesis uses only light energy and simple inorganic substances, and involves many stages controlled by enzymes.

Since photosynthesis is a light dependent reaction, the intensity of light should affect the rate of photosynthesis.  As one of the products of photosynthesis is oxygen, therefore the oxygen concentration will be measured to show the effects of photosynthesis.


Aim: to find the effect of light intensity on the rate of photosynthesis of Canadian pondweed (Elodea Canadensis).

Hypothesis: as the light intensity decreases, the rate of photosynthesis should also decrease.

Variables: light intensity (independent variable) will be altered by changing the distance between the lamp and the plant, hence the rate of photosynthesis (dependent variable) will be measured by measuring the volume of oxygen produced by the plant in 10 minutes.

Table 1 Controlled variables.

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  1. Photosynthometer:

        syringe, plastic tube,

        measuring pipette,

        funnel, test tube,         beaker;

  1. Clamps and Stand;
  2. Elodea Canadensis;
  3. Razor blade;
  4. NaHCO3  powder;
  5. Scales;
  6. Distilled water;
  7. Beaker;
  8. Thermometer;
  9. Lamp (20W);
  10. Stopwatch.


The experiment was done in the dark room. 5g of NaHCO3 was measured using scales and put into 250mL of distilled water. Then, 10 centimeters of Elodea was cut using razor blade and immediately put into the carbonate-filled test tube with the cut end kept up. Test tube with the Elodea was put into the beaker filled with water in order to ...

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